Ukrainian prime minister, Arseniy Yatsenyuk, has declared his country “on the brink of disaster”.
The statement came shortly before Ukraine’s acting president, Oleksander Turchynov, announced the closure of Ukrainian airspace to any non-civilian aircraft.
Meanwhile, people have gathered in Independence Square, the scene of many of the recent protests in the capital, Kyiv.
“We need international support, not just expressions of concern,” said one man in the square. “We need more definite steps.”
“I think the United Nations, USA and European Union should help us,” said Nadia, a resident of Lviv. “And I want to leave for another continent far away from Russia to avoid this problem.”
Kyiv has now asked for international aid, particularly to help protect its nuclear assets.
NATO’s Secretary General, Anders Fogh Rasmussen, has responded, calling on Russia to de-escalate tensions.
Ambassadors from NATO will meet in Brussels on Sunday to discuss the situation.